Guides · Treadmill pace vs road pace
Treadmill pace vs road pace: why the same effort feels different
You run 9:00 pace on the road and it feels like work. You set the belt to the same 9:00 and your legs ask what the problem is. Some days it flips, and the belt feels brutal at a speed you cruise outside. Two separate things cause that, and a pace conversion only handles one of them.
Quick answers
Is treadmill pace the same as road pace? No. At the same speed, running indoors costs you less energy than running outdoors, because there is no air to push through. A 1996 study in the Journal of Sports Sciences found that a 1% treadmill grade made the energy cost of the two match for paces between about 5:22 and 9:11 per mile.
Should I run at 1% incline on a treadmill? If you run faster than about 9:11 per mile, 1% is a fair way to match flat road effort. Slower than that, air resistance barely matters, so a flat belt is fine. The rule came from trained male runners at 5-minute efforts, so treat it as a good default rather than a law.
Why does the treadmill feel harder if it takes less energy? Cooling is a large part of it. Running outdoors you generate your own wind, and a 2024 wind tunnel study of 14 participants found that this self-generated cooling does not carry over to an indoor treadmill. You make the same heat on the belt with less moving air to take it away.
Does a treadmill pace conversion make my numbers accurate? No. A conversion adjusts for effort. It cannot check the belt. If the belt is moving slower than the display claims, the converted pace carries that error straight through.
How do I find my real treadmill pace? Measure the belt itself. The display reports the speed the motor was told to hold, not the speed the belt is really moving, so the only honest number comes from measuring the belt directly.
What the air is doing to you outside
Every step you take outdoors pushes a small wall of air out of the way. On a treadmill that cost disappears, because the air in the room is standing still.
In 1996, nine trained male runners ran six speeds, from about 9:11 down to about 5:22 per mile, on a treadmill at several inclines and on a level road. A 1% treadmill grade made the energy cost of the belt match the road across that whole range. That is the 1% rule, and it applies to a specific band of paces.
What to set, by the pace you actually run
Belt speed, the pace it works out to, and whether the 1% rule was tested there.
| Belt speed | Pace per mile | Set the incline to |
|---|---|---|
| 5.0 mph | 12:00 | Flat is fine, you move too little air to matter |
| 6.0 mph | 10:00 | Flat is fine |
| 7.0 mph | 8:34 | 1% |
| 8.0 mph | 7:30 | 1% |
| 10.0 mph | 6:00 | 1% |
| 12.0 mph | 5:00 | 1% is reasonable, though it is faster than the study measured |
The tested band was 5:22 to 9:11 per mile, using trained male runners over efforts of about 5 minutes. Every pace in this table assumes the belt speed is real, which is the second half of this article.
Why it still feels harder some days
Less energy on paper does not mean easier in the moment. Outdoors you generate your own wind, and that moving air cools you. A 2024 wind tunnel study of 14 participants found that this self-generated cooling does not carry over to an indoor treadmill. You make the same heat on the belt with less air to carry it away.
The same speed, two different runs
Why the belt can cost less energy and still feel worse.
Easier indoors
- No air to push through
- No hills unless you add them
- No wind, no rough footing, no stops
Harder indoors
- No self-generated wind, so less cooling
- One exact speed held for the whole run, with no natural drift
- No changing terrain, weather or scenery
A 1% incline answers the left column. Nothing on the right column is fixed by a number.
The conversion everyone uses, and what it assumes
Pace conversion charts take a treadmill speed and an incline and hand back a road pace. The math is sound, but every chart assumes the speed you typed in is true. The number on your treadmill is a command sent to the motor rather than a reading taken off the belt.
A well-kept machine follows that command closely. A 2021 study in Scientific Reports measured four treadmills and found average belt speeds between 98% and 103% of the set speed. Even in that range the pace you see is a little off, and nothing on the display tells you which way.
What a small error does to your converted pace
A runner sets 6.0 mph for a tempo mile on a machine running 2% slow, which published testing puts in the good range.
This is an illustrative example, not a logged test. The plan called for a 10:00 tempo mile, so that workout never happened at the pace it was written for, on a machine nobody would call broken.
Converting that 10:00 to a road pace does not help, because the arithmetic starts from a wrong number. Machines further out than 2% exist, and we have measured some of them.
What we found when we measured
We check treadmills with a handheld contact tachometer, which reads the belt's true surface speed directly instead of asking the machine what it thinks. For one machine we used the tachometer speed table we had already built for it.
On one machine, the display claimed 2.3 miles for a run that was really 2.0, which is 15% of that run credited to a runner who never covered it. The next day, the same machine read 5.6 miles against a real 5.0, and an Apple Watch on the runner's wrist agreed with the display rather than catching it. Indoors a watch has no GPS to check against, so agreement between the two proves nothing.
Some machines are honest, but nobody audits gym equipment, so no one can say how common that is. An honest machine and a machine 15% out show you the same confident number, so there is no bias you can learn and subtract.
How to compare the two honestly
- Match your effort and let the number go. Run by feel or heart rate. This is free and it works, but it leaves you with no pace data to train against.
- Count belt laps. With a tape measure and a stopwatch, you can time how long the belt takes to go around and work out its real speed. It costs nothing, though you spend the time counting instead of running. More on this method.
- Measure it with your phone. It takes a few seconds on any machine, including one at a gym you have never used. A contact tachometer is more accurate than a phone, but you have to buy one.
Treadwell reads the belt's real speed through your iPhone's camera and LiDAR sensor. You hold the phone over the moving belt from beside the machine and it measures the belt directly. On a hotel treadmill it had never seen, its reading landed within half a percent of a handheld tachometer. If it cannot get a reading it trusts, it says so instead of showing a made-up number. It needs an iPhone Pro, because those carry the LiDAR sensor.
Know what your indoor paces actually mean
See the pace your belt really runs, so your indoor paces mean what you think they mean. You need an iPhone Pro.
Scan with your iPhone Pro to get the appTested: in our tachometer tests the app read within about 2 percent of true belt speed.
Set the incline, then check the number
Put the belt at 1% if you run faster than about 9:11 per mile, which squares the effort against the road. Then find out what your belt is really doing, because effort was only half the gap.
Sources.
- The 1% grade finding and its tested speed range: Jones AM and Doust JH, "A 1% treadmill grade most accurately reflects the energetic cost of outdoor running," Journal of Sports Sciences 14(4):321-327 (1996). Nine trained male runners at speeds from 2.92 to 5.0 metres per second.
- Self-generated wind cooling you outdoors, and that benefit not carrying over to an indoor treadmill: Yamashita N, Ly CL, Smallcombe JW, Hodder S and Havenith G, "Air speed and direction affect metabolic and thermoregulatory responses during walking and running in a temperate environment," Journal of Applied Physiology 137(3):554-568 (2024). Wind tunnel study, 14 participants.
- Belt speed against set speed: Willwacher et al., Scientific Reports 11:2244 (2021). Four treadmills, average belt speeds 98% to 103% of target.
- The 2.3 against 2.0 run and the hotel treadmill result are our own tests, checked against a handheld contact tachometer on the day.
- The 5.6 against 5.0 run is our own test, checked against that machine's standing tachometer table rather than a fresh tachometer reading that day.
- The hotel treadmill figure is the accuracy of our own reading against the tachometer on a machine we had never measured before. It is not a statement about that treadmill's display.
- The 6.0 against 5.88 worked example walks through the arithmetic. Nobody ran that mile on a belt to log it.